The invention relates to an apparatus for the measurement of the drive torque exerted on a drivable wheel, in particular on the drive wheel of a bicycle, and/or for the measurement of parameters associated therewith the apparatus being of the kind comprising a wheel hub which is rotatably journalled relative to a fixed axle; a drive axle which is coaxially disposed between the fixed axle and the wheel hub; a member which permits a relative rotation disposed between the drive axle and the wheel hub at the drive side end; a fixed connection formed at the other end between the drive axle and the wheel hub; a device for detecting the relative rotation between the wheel hub and the drive axle which depends on the drive torque and also for generating signals representative of the relative rotation and suitable for evaluation.
For the improvement of physical performance the bicycle is increasingly used in the field of sport as a special training apparatus, and moreover bicycles are increasingly used, in particular in a stationary embodiment, for the treatment and rehabilation of patients with heart and circulatory illnesses. In carrying out such training and treatment programs it is important to obtain information relative to the power developed by the particular sportsman or patient and the energy consumed, since this information makes it possible to draw conclusions on the training or treatment results.
It is already known from DE-A1 31 50 149 to achieve a largely loss-free power measurement by providing a resilient connection between a driven wheel of a transmission and a component to be driven and to measure the angle of rotation which arises on applying drive forces to the transmission wheel through the relative rotation between the transmission wheel and the component to be driven. Pulse sequences are thereby generated by means of two measurement transducers, with the time separation between the pulses of these measurement transducers being evaluated as a measure for the power which is transmitted. A disadvantage of this known apparatus is above all the fact that the measurement accuracy which can be achieved left much to be desired as result of the difficulty of detecting the very small angle of rotation which amounts to a maximum of 1 to 2 degrees.